What am I?

RAY: Car parts have changed composition over the years. For example, the wheels of cars used to be made with wooden spokes, and then they evolved into steel. Now, most wheels are made out of some kind of magnesium-aluminum alloy. Dashboards used to be made out of wood, and now they're made out of steel.

Now I'm going to tell you what I used to be made out of and you're going to tell me what I am. Here it is:

"In the early days of cars, I didn't even exist. When they saw a need for me, I was first made out of wood. Later on, when they discovered that wood didn't work too well, I was made out of leather. Some time later, I was made out of cotton. Today, I am made out of a mixture of things, some of which are steel wool, iron, and bronze."